Industrial and domestic emergency generators use three-phase electric motors. All three outputs carry the same current and the power transfer remains constant, resulting in a linear and balanced load. To convert the power to amperes, you need to know the voltage and power ratios of the electric motor. Power factor determines the delay between voltage and actual current of an electrical current. Most large three-phase motors have this rating on their identification plate.

First, make sure your measurements are in standard units. For a motor or generator in kilowatts, convert power to watts: 1 kW = 1000 W.

Get voltage measurement if not already done. Use a quality digital voltmeter to measure line voltage between any two of the three outputs.

Find the power factor (CF) on the nameplate. For a purely resistive circuit, the power factor is 1.0 (ideal).

Use Ohm's Law formula: power (watts) = voltage (volts) x current (amperes).

Equate the three-phase power to obtain the current (in amperes). Current (ampere) = power (W) ÷ voltage (volts) ÷ square root of 3 (1.732) ÷ power factor; I = P ÷ (V_1,732_k.m.).

Plug in the power to be converted (in watts), the voltage (in volts) and the power factor to find the current (in amperes. power factor 0.8:

I = 1141000 ÷ (4401.732 x 0.8) = 187 A. That is, the current is 187 amperes.

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